This invention relates to improvements in those recording apparatuses where a recording medium such as paper is supported by a platen for contact with a recording element such as an electrostatic or thermal printhead. The invention is particularly well suited for use with moving head printers having "soft" platens rather than "hard" platens.
Hard platens are rigid and do not deform under the pressure of contact with the printhead. They are generally made of a nonpliable plastic, or of metal. Any irregularity in a hard platen will lessen the degree of contact between the printhead and the recording medium, resulting in a decrease in the quality of the printed result.
Although hard platens are often satisfactory, it has been found that moving head printers, and particularly thermal moving head printers, can often produce a result of significantly improved quality if a soft platen is used. A soft platen is a strip of resilient and pliable material, such as silicone rubber, supported upon a rigid member. However, a concomitant disadvantage has been that soft platens exhibit a high degree of friction with the recording medium, making it more difficult to advance the paper once a line has been printed. A common solution to this problem of increased friction has been to release the pressure between the platen and the printhead during paper advance. However, this complicates the mechanism, reduces reliability, and increases power requirements.
An additional concern in the design of a recording apparatus that automatically loads its recording medium is the integrity of the path for the recording medium. Particularly in printers, the path is apt to have severe bends, and the platen itself may act as an obstruction upon which the paper may snag during loading.
Accordingly, a principal object of the present invention is to provide a way to employ a soft platen in a recording apparatus without incurring increased friction between the platen and the recording medium.
Another object of the invention is to provide a long lasting low friction barrier suitable for use with a soft platen.
A further object of the invention is to provide a means of overcoming obstructions in the paper path of recording apparatuses.
These objects of the invention are met in a recording apparatus that incorporates a flexible low friction platen cover that overlaps the platen in a direction the same as the direction in which the recording medium is advanced. In a preferred embodiment for a moving head thermal printer having a soft platen the flexible platen cover is a sheet of Teflon.RTM. impregnated cloth woven of glass fibers. The sheet is attached to the frame at a location along the paper path preceeding the platen, but not directly in the path. The sheet is draped over the platen and overlaps it. The sheet thus serves both to funnel an advancing edge of the paper (during loading) past the platen, as well as to reduce friction between the soft platen and the paper. Because of the flexible nature of a Teflon.RTM. impregnated woven glass fabric the superior printing characteristics of a soft platen are retained. Because of the lubricating effect of the Teflon.RTM., the friction is greatly reduced, while at the same time the hardness and wear resistance of the glass gives the platen cover long life.